Separation of fatty acids from rosin acids



latented Mar. 14, 1944 SEPARATION or FATTY Aorps FROM ROSIN ACIDS Arthur W. Hixson, Leonia, N. J., and'Ralph Miller, New York, N. Y., assignors to The Chemical Foundation, Incorporated, a corporation of Delaware No Drawing. Application April 28, 1940,

Serial No. 331,159

11 Claims.

This invention is concerned with the fractionation of tall oil.

In our copending application Serial No. 264,780, filed March 29, 1939, we have described a process of refining and fractionation of tall oil. As therein explained, crude tall oil contains many complex bodies in addition to organic acids; and among the complex bodies which are particularly objectlonableis a small amount of tar and pitch. The first step in the process described herein is similar to the first step of our prior invention. That is, the pitch and tar are removed from tall oil by heating a solution composed of tall oil dissolved in a liquefied, normally gaseous, hydrocarbon until a rosin phase starts to precipitate. A constant temperature is maintained and the rosin phase separated from the hydrocarbon solution.

This removal of a small quantity of rosin in this.

fashion effectually removes most of the tar and pitch.

Whereas in our prior application the subsequent operability of the process there set forth and described essentially involves a, rise in operating temperature, we have also discovered that rosin acids are less soluble in liquefied, normally gaseous, hydrocarbons at reduced temperatures than fatty acids. This present application is predicated upon that discovery and others, as next noted, as embodied in a p o dependent essentially upon the lowering of temperatures for operability. i

Contrary to prior knowledge, we have discovered that rosin acids have only a limited solubility in liquefied, normally gaseous, hydrocarbons. In fact, by judicious choice of hydrocarbon solvent, and proper selection of the ratio of solvent to tall oil, some rosin crystals will precipitate when the hydrocarbon solventis added to tall oil at a temperature a little below room temperature. Propane used at a ratio of 8 to 1 at a temperature a little below room temperature will fulfill the conditions.

This discovery is the more surprising in view of the disclosures of Rankin and Waligora in U. S. Patents Nos. 2,117,572 and 2,142,592. These inventors indicate that rosin acids are very soluble in liquefied, normally gaseous, hydrocarbons. See Rankin, page 2. column 2, lines 6 to-l0, and Waligora, page 1, column 1. lines 35 and 36, as a presentation of the state of the prior knowledge in this field.

Our present invention depends upon these two hitherto unknown facts. If the temperature of the hydrocarbon solution of tall oil is slowly reduced, well-defined crystals of rosin will precipitate. By precipitating crystals of rosin in this manner in the absence of tar and pitch, lightcolored relatively large crystals are formed. A suitable ratio of volume of solvent to volume of tall oil treated is about 8 to 1. More than of the rosin is in the form of crystals by the time the temperature is reduced to 10 F. By this method the fatty acids can be practically separated from the rosin acids. Because the rosin acids separate as well-defined crystals, the only impurity that can contaminate them must be adsorbed on the surface of the crystals. The larger the crystals, the smaller the surface for a given weight of rosin. Therefore, the amount of undesirable, adsorbed material will decrease as the crystal-size increases. The crystals are readily washed with pure solvent and the larger the crystals, the more easily are they washed.

Liquefied, normally gaseous, hydrocarbons not only permit the tar and pitch to be readily removed; as mentioned above, but also, by their se lective solvent action, permit rosin acids to be separated from fatty acids at reduced temperatures. A third function that can be performed by these useful solvents in treating tall oil, is to act as a refrigerating medium. The temperature of the hydrocarbon solution of tall oil can be reduced to any required degree and at any required rate by the controlled vaporization of the solvent. Thus, these solvents have a triple function, each of which is important, and eachcontributes to the utility of our novel process.

Our preferred solvents are propane and isobutane although ethane, butane, and the corresponding unsaturated compounds can be employed. Any mixture of these hydrocarbons can be used. The enormous difierence in volatility.

between the constituents of tall oil and the hydrocarbons employed as solvents, pennits the ready separation of the hydrocarbons from the tall oil fractions by distillation. The hydrocarbons ar removed and recovered, thus insuring very low solvent losses. The distilled hydrocarbons are returned to the process at the pitchremoving step or as crystal wash-liquor.

The hydrocarbon solution of fatty acids may be advantageously subjected to distillation to recover the solvent and improved fatty acid. A combination process utilizing all our discoveries may be employed. This combination process produces pure fatty acids and pure rosin in very high yields. As a rsum of the novel steps: After removal of pitch and tar, the solution is then chilled to precipitate rosin acids. The rosin acids are separated from the hydrocarbon solution. The hydrocarbon solution is heated up to the point where all the rosin acids still in solution are precipitated as a second liquid phase. This second liquid phase is separated from the hydrocarbon solution and returned to the rosin precipitation step. The hydrocarbon solution is distilled to recover the hydrocarbon solvent and pure fatty acids.

Another method of utilizing these hitherto unknown facts is to treat tall oil with a liquefied, normally gaseous, hydrocarbon at a low temperature. Temperatures in the neighborhood of 40 F. are suitable. Under such conditions, the fatty acids present in tall oil are much more soluble in the hydrocarbon solvent than the rosin acids. The rosin acids will appear as small crystals insoluble in the hydrocarbon solvent. The crystals can be readily separated from the fatty acid hydrocarbon solution. By employing suitable contacting equipment this extraction can be carried out in a counter-current fashion at still lower temperatures, thus insuring the absence of rosin acids from the hydrocarbon solutions. The fatty acids which dissolve in the liquefied, normally gaseous, hydrocarbonsare recoverable by distilling the solution to evaporate the solvent from the comparatively non-volatile fatty acids.

We claim: I

l, The process of treating tall oil comprising in dissolving the tall oil in a liquefied, normally gaseous. hydrocarbon, warming the solution until a rosin phase starts to precipitate, maintaining the temperature constant until the rosin phase, which will include most of the tar'and pitch, is separated from the hydrocarbon solution, cooling the hydrocarbon solution until nearly all the rosin has precipitated as a solid, separating the solid rosin from the hydrocarbon solution, and distilling the solution to recover the hydrocarbon solvent and a fatty acid fraction.

2. The process of treating tall oil comprising in removing the tar and pitch present by the use of a liquefied, normally gaseous, hydrocarbon, chilling the resultant solution until the rosin acids precipitate as a solid, separating the solid rosin from the hydrocarbon solution, warming the hydrocarbon solution until all the rosin acids still in solution precipitate as a second liquid phase, separating the rosin liquidphase, and treating the hydrocarbon solution to recover the fatty acids and the solvent.

3. The process of treating tall oil comprising in removing the tar and pitch present by the use of propane, chilling the resultant solution until the rosin acids precipitate as a solid, separating the solid rosin from the hydrocarbon solution, warming the hydrocarbon solution until all the rosin acids still in solution precipitate as a second liquid phase, separating the rosin liquid phase, and treating the hydrocarbon solution to recover the fatty acids and the solvent.

4. The process of treating tall oil comprising in removing the tar and pitch present by the use of a mixture of liquefied, normally gaseous, hydrocarbons, chilling the resultant solution until the rosin acids precipitate as a solid, separating the solid rosin from the hydrocarbon solution, warming th hydrocarbon solution until all the rosin acids still in solution precipitate as a second liquid phase. separating the rosin liquid phase, and treating the hydrocarbon solution to recover the fatty acids and the solvent.

5. In the fractionation of tall oil process of separating rosin acids from fatty acids dissolved in a liquefied, normally gaseous, hydrocarbon comprising in vaporizing part of the solvent to chill the solution, thus causing the precipitation of the rosin acids as crystals, separating the crystals from the solution, and treating the solution to recover the hydrocarbon and the fatty acids.

6. In the fractionation of tall oil process of separating rosin acids from fatty acids dissolved in propane, comprising in vaporizing part of the solvent to chill the solution, thus causing the precipitation of the rosin acids as crystals, separating the crystals from the solution, and treating the solution to recover the hydrocarbon and the fatty acids.

'7. In the fractionation of tall oil process of separating rosin acids from fatty acids dissolved in a mixture of a liquefied, normally gaseous, hydrocarbons comprising in vaporizing part of the solvent to chill the solution, thus causing the precipitation of the rosin acids as crystals, separating the crystals from the solution, and treating the solution to recover the hydrocarbon and the fatty acids.

8. The process of treating tall oil comprising in separating the tar and pitch present by means of a liquefied, normally gaseous, hydrocarbon, vaporizing a portion of the hydrocarbon to chill the remainder of the solvent and thereby obtaining rosin crystals, separating the crystals from the solution, warming the solution until any rosin present forms a second liquid phase, separating the rosin liquid phase from the hydrocarbon phase, and treating the hydrocarbon pliase to recover a fatty acid fraction and the hydrocarbon.

9. The process of treating tall oil comprising in separating the tar and pitch present by means of propane, vaporizing a portion of the hydrocarbon to chill the remainder of the solution and thereby obtaining rosin crystals, separating the crystals from the solution, warming the solution until any rosin present forms a second liquid phase, separating the rosin liquid phase from the hydrocarbon phase, and treating the hydrocarbon phase to recover a fatty acid fraction and the hydrocarbon.

10. The process of treating tall oil comprising in separating the tar and pitch present by means of a mixture'of liquefied, normally gaseous, hydrocarbons, vaporizing a portion of the hydrocarbon to chill the remainder of the solution and thereby obtaining rosin crystals, separating the crystals from the solution, warming the solution until any rosin present forms a second liquid phase, separating the rosin liquid v phase from the hydrocarbon phase, and treating the hydrocarbon phase to recover a fatty acid fraction and the hydrocarbon.

11. The process of treating-tall oil comprising in separating the tar and pitch present by means of liquid propane, vaporizing a portion of the hydrocarbon to chill the remainder of the solution to a temperature between substantially '40" F. and minus 10 F. to thereby obtain rosin crystals, separating the crystals from the solution and recovering fatty acids from the solution.

ARTHUR W. HIXSON. RALPH IVHLLER. 

